Wireless communication method and radio network controller for coordinating paging occasions on a common paging channel

ABSTRACT

A method of paging a plurality of users by synchronizing user equipment (UE) specific paging and Point-to-Multipoint (PtM) user group paging to reduce power consumption when the UE is in a discontinuous reception state. The UE identities are defined such that paging occasions and common paging channels are synchronized for multiple users within a PtM user group.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/630,892, filed Jul. 30, 2003, which issued as U.S. Pat. No. 7,197,323on Mar. 27, 2007 and claims the benefit of Provisional Application No.60/400,591, filed on Aug. 1, 2002, which are incorporated by referenceas if fully set forth.

FIELD OF INVENTION

This present invention generally relates to the field of wirelesscommunications. More particularly, the present invention relates toproviding paging services and mechanisms in cellular networks.

BACKGROUND

In conventional 3^(rd) Generation (3G) Cellular Networks, Point-to-Point(PtP) and Point-to-Multipoint (PtM) paging mechanisms need to provideefficient use of radio paging resources while maintaining low UserEquipment (UE) power consumption. Paging is used to establishconnections and initiate transmissions. For PtP services, a pagingsignal that is transmitted to a UE is associated a unique identityassigned to the UE. It is expected for UEs to be in an inactive pagingstate for considerable time periods while awaiting paging indications.Thus, it is necessary to minimize power consumption while the UEs are insuch a paging state. To accomplish this, paging occasions arepredetermined in the UE and network. This allows the UE to minimizetransmit and receive processing between paging occasions, which resultsin reduced power consumption and correspondingly increased battery life.

For PtP services, a physical paging channel and paging occasion isdetermined from identities unique to each UE. A motivation for using UEidentities is to provide a substantially equal distribution of pagingtransmissions across all paging resources.

System Information Block type 5 (SIB 5) defines common channels to beemployed in an “idle” mode, and SIB 6 defines common channels for a“connected” mode. In a cell, one or more Paging Transport Channels(PCHs) may be established. Each Secondary Common Control PhysicalChannel (SCCPCH) indicated to the UE in system information may carry upto one PCH. Thus, for each defined PCH there is one uniquely associatedPage Indicator Channel (PICH) also indicated. When more than a singlePCH and associated PICH are defined in SIB 5 or SIB 6, the UE selects aSCCPCH from the ones listed in SIB 5 or SIB 6 based on an InternationalMobile Subscriber Identity (IMSI) as follows:Index of selected SCCPCH=IMSI mod K;  Equation (1)where K is equal to the number of listed SCCPCHs which carry a PCH(i.e., SCCPCHs carrying a Forward Access Channel (FACH) only shall notbe counted). These SCCPCHs are indexed in the order of their occurrencein SIB 5 or SIB 6 from 0 to K−1.

Thus, the UE selects a physical paging channel from a list of pagingchannels according to a Selected Paging Channel Number as follows:Selected Paging Channel Number=UE identity mod K;  Equation (2)where K is the number of physical paging channels that exist within thecell. Equation (2) randomly distributes UEs between the paging channels.

The UE may use Discontinuous Reception (DRX) in idle mode or connectedmode in order to reduce power consumption. When DRX is used, the UEneeds only to monitor one Page Indicator (PI) in one Paging Occasion perDRX cycle. The UE may be attached to different Core Network (CN) domainswith different CN domain specific DRX cycle lengths. The UE stores eachCN domain specific DRX cycle length for each CN domain the UE isattached to and use the shortest of those DRX cycle lengths. The DRXcycle lengths to use for Universal Terrestrial Radio Access Network(UTRAN) connected mode is the shortest of the following:

(1) the UTRAN DRX cycle length; or

(2) any of the stored CN domain specific DRX cycle lengths for the CNdomains the UE is only attached to with no signaling connectionestablished.

The UE uses the IMSI, the number of available SCCPCH which carry a PCH(K), the Cell System Frame Number (SFN), Np, frame offset, Paging BlockPeriodicity (PBP) and the DRX cycle length to determine the pagingoccasions.

For Frequency Division Duplex (FDD), Np is the number of page indicatorswithin a frame, and the frame offset is equivalent to zero. In FDD, theUE monitors its paging indicator in the PICH frame with SFN given by thePaging Occasion.

For Time Division Duplex (TDD), Np is the number of page indicatorswithin a paging block and PICH frame offset values are given in systeminformation.

In TDD, the UE monitors its paging indicator in the paging block givenby the paging occasion. The paging occasion gives the SFN of the firstframe of the paging block.

The value of the Paging Occasion is determined as follows:Paging Occasion={(IMSI div K) mod (DRX cycle length div PBP)}*PBP+n*DRXcycle length+Frame Offset;  Equation (3)where n=0, 1, 2 . . . as long as SFN is below its maximum value. Theactual Page Indicator within a Paging Occasion that the UE shall read issimilarly determined based on IMSI.

The Page Indicator to use is calculated by using the following formula:PI=DRX Index mod Np;  Equation (4)where DRX Index=IMSI div 8192.

In TDD mode, the Paging Message Receiving Occasion is calculated usingthe following formula:Paging Message Receiving Occasion=Paging Occasion+N _(PICH) +N_(GAP)+{(DRX Index mod Np) mod N _(PCH)}*2;  Equation (5)where the value N_(PICH) is the number of frames for PICH transmissionand is equal to the PICH repetition length given in system information.The value N_(GAP) is the number of frames between the last framecarrying PICH for this Paging Occasion and the first frame carryingpaging messages for this Paging Occasion. The value N_(PCH) is thenumber of Paging Groups. N_(PCH) and N_(GAP) are given in systeminformation.

Thus, the UE determines the paging occasion, identified by a uniqueradio frame number, on the selected PICH according to:Paging Occasion Frame Number={UE identity div K} mod {DRX CycleLength}+n*{DRX Cycle Length};  Equation (6)where DRX is Discontinuous Reception.

Equation (6) identifies the frame number within each DRX cycle and thenfor each following cycle.

In TDD systems, paging block periodicity and frame offset are also takeninto account. A motivation for using UE identities is to provide anapproximately even distribution of paging transmissions across allpaging resources.

FIG. 1 illustrates a problem with group paging where the UE will likelyhave to receive separate paging occasions and physical paging channelsfor reception of user group and UE specific paging. In FIG. 1, “UP” 105represents a UE specific paging occasion; “GP” 110 represents a UserGroup paging occasion; and “X” 115 represents UE in DRX. A moreefficient method for performing group paging is desired.

SUMMARY OF THE INVENTION

The present invention defines a UE paging mechanism that synchronizesuser specific and user group paging opportunities for support ofbroadcast and multicast services. The paging mechanism coordinatespaging occasions for user specific and user group on a common pagingchannel. The present invention applies group paging for PtM service tosimilar paging channel and occasion determination logic such that the UEidentity in the above Equations (2) and (6) is replaced by a common usergroup identity. This allows for one paging channel and set of pagingoccasions to be associated with a particular PtM user group. The benefitof PtM user group paging is physical resources used for paging withineach cell are only required once per user group, rather than once peruser in the group.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of preferred embodiments, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a block diagram illustrating conventional independent userspecific and user group paging occasions on separate physical pagingchannels;

FIG. 2 is a block diagram illustrating coordinated user specific anduser group paging occasions on a common paging channel in accordancewith the present invention;

FIG. 3 is a flow chart including method steps of paging a plurality ofusers using a temporary identity to synchronize paging services inaccordance with one embodiment of the present invention;

FIG. 4 is a flow chart including method steps of paging subsets of aplurality of users in accordance with another embodiment of the presentinvention; and

FIG. 5 is a Radio Network Controller (RNC) for coordinating userspecific and user group paging occasions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention defines a UE paging mechanism in a wireless systemthat synchronizes user specific and user group paging opportunities byforcing a PCH and paging occasion to be at the same instance so that theusers can conserve battery and so that the paging channel is used moreefficiently. On the PCH are paging occasions where, for a certain pagingperiod, the paging mechanism only has to wake up once within that periodto look for a paging message. This results in a reduction of UE powerconsumption because the paging mechanism does not have to continuouslymonitor the PCH separately for the PtP and PtM paging occasions.

Hereafter, a UE is a wireless transmit/receive unit (WTRU) that includesbut is not limited to a mobile station, fixed or mobile subscriber unit,pager, or any other type of device capable of operating in a wirelessenvironment.

In accordance with the present invention, the specific channels and thepaging occasions on the channels are always known by the UE and by thenetwork. As shown in FIG. 2, there is disclosed a mechanism thatcoordinates paging occasions for specific users and user groups on acommon paging channel. In this Figure, the terminology UP refers to a UEspecific paging occasion; GP refers to a User Group paging occasion andX refers to the UE in DRX mode.

Referring to FIG. 3, a procedure 300 in accordance with the presentinvention is shown. A common identity management function, orcoordination between user group and user specific identity managementfunctions, provides identities that correlate to common paging channelsand paging occasions. In accordance with the procedure 300, newtemporary user specific identities are assigned upon activation of a PtMservice for all UE's within a PtM user group (step 305). The temporaryuser specific identities correlate to the same physical paging channeland paging occasion associated with group paging.

In step 310, the UE selects a physical paging channel from a list ofpaging channels. The paging channel is selected according to:Selected Paging Channel Number=UE temporary identity mod K;  Equation(7)where K is the number of physical paging channels that exist within thecell.

The UE then determines the paging occasion, identified by a unique radioframe number, on the selected PICH (step 315), where:Paging Occasion Frame Number={UE temporary identity div K} mod {DRXCycle Length}+n*{DRX Cycle Length};  Equation (8)

The paging channel and paging occasions may continue to be determinedfrom the low order bits of the assigned identities. In this case, thehigh order bits may be used to distinguish UE specific and user grouppaging causes.

In accordance with the present invention, UEs have a common pagingoccasion for both user specific and PtM user group paging. There is noneed to increase the number of paging occasions upon activation of thePtM service. Correspondingly, there is no need for an increase in powerconsumption upon activation of the PtM service.

Upon the occurrence of a paging occasion, the UE checks for both the UEspecific paging identity and the PtM user group identity. Depending onthe received identity, the type of paging is known to the UE.Alternatively, it is possible to provide a common identity and determineUE specific or PtM group paging in the associated signaled paging cause.Thus, when the UE reads on its paging occasion, it reads both theidentity being paged and a paging cause, either of which may indicatethe type of service (PtP or PtM).

Depending on the maximum number of users per paging occasion, it may benecessary to distribute user specific paging occasions for the usergroup across more than one physical paging channel and paging occasion.For large PtM user groups, several PtM identities can be provided sothat individual paging occasions are not saturated. Each PtM identity isassociated with a paging subgroup within the PtM user group.

A subgroup paging identity is generated for each physical paging channeland associated paging occasion required for the PtM user group. When PtMuser group paging is required, each subgroup paging identity is appliedto its associated paging channel and paging occasion.

As previously described, a UE identity is used for determining thepaging channel and the paging occasion. The present invention providespaging for PtM services provided for a plurality of member users.Normally, these users have different paging channels and differentoccasions. One of the goals of the present invention is create an evendistribution of paging occasions across the PCH so that physicalresources are efficiently allocated. Otherwise, if pages are not evenlydistributed, there will be periods in which the PCH is not fullyutilized. An excess of pages occurring during a particular pagingoccasion will cause an page overflow and opportunities to page the UEfor the paging occasion are lost.

The user identity is used to create an even distribution. For PtMservices provided for a number of users having UEs that have to wake upand recognize a page, the present invention minimizes the amount ofpaging. For example, if the PtM services fifty users, it would beundesirable to page all fifty of those users independently. The presentinvention executes one set of page occurrences generated by the networkby using a single set of paging occasions that are used for waking upthe UEs of the fifty users in order to receive the service.

In the preferred embodiment of the present invention, PtM services aresynchronized whereby a temporary identity is used to synchronize pagingoccasions of both PtP and PtM services. A temporary identity isgenerated for each PtM and PtP service, or a common identity may beestablished for both (e.g., when a paging cause or some method otherthan “high order bits” is used to determine PtP or PtM). Only the lowerorder bits of the paging identity or UE identity are used to determinewhat the paging occasion is. The high order bits may be used todetermine whether PtP or PtM services are to be used. When a UE receivesa page, a match on the UE specific paging identity occurs. Thus, notonly is it necessary to find a paging occasion on whatever pagingchannel that is assigned to the UE, but when the paging occasion isexamined, a paging identity is examined that indicates whether theservice is PtP or PtM by the value that is signaled at the pagingidentity. Alternatively, there is also a paging cause that is receivedalong with the paging identity. The paging cause signals the userwhereby a common identity is identified and the associated paging causeis examined to determine whether the service is PtP or PtM.

For a very large number of users in a PtP group (e.g., 1000 users), whenthe particular paging occasion is forced to align with the PtM pagingoccasion, too many PtP paging occasions or users may exist at the samepaging occasion, resulting in the saturation of that paging occasion.Furthermore, the distribution of users across all available pagingoccasions is lost. Thus, it is undesirable to have all of the pagingoccasions for a large number of users to be focused on one pagingoccasion.

Referring to FIG. 4, the UE selects a physical paging channel from alist of paging channels (step 405) in accordance with the procedure 400.The paging occasions are set by keeping track of the paging channels andpaging occasion assignment logic. More than one PtM paging occasion iscreated for very large groups. Groups of the users that are associatedwith this PtM group are associated with respective ones of the PtMpaging occasions. For example, if there are presently 1000 users butonly a maximum of 100 of the users are permitted to be associated withany one paging occasion, 10 paging occasions having 100 users associatedwith each are established, so that the UEs associated with those 100users will wake up at the time they normally would at that pagingoccasion and look for either the PtP or the PtM identifiers to determinewhat service is being initiated (step 410). It necessary to limit thenumber of UEs per paging occasion because for PtP services, pagingchannels and paging occasions would not be evenly distributed. Of the1000 users that are listening, groups of 100 will focus on certainpaging occasions, so that when the PtM service is established, ten pagesare generated, one for each group of 100 users (step 415).

Referring to FIG. 5, a Radio Network Controller (RNC) 500 determines howthe paging occasions are set by keeping track of the paging channels andpaging occasion assignment logic. The RNC 500 includes a common identitymanagement function device 505, a paging channel tracking device 510, apaging occasion assignment logic device 515 and a paging channelsgeneration device 520. The common identity management function device505 provides identities that; correlate to common paging channels andpaging occasions. The paging channel tracking device 510 sets the pagingoccasions by keeping track of the paging channels. The paging occasionassignment logic device 515 keeps track of the paging occasionassignment logic. The paging channels generation device 520 associatesgroups of the users of a PtM group with respective ones of the PtMpaging occasions.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention as describedabove.

What is claimed is:
 1. A method of paging comprising: establishing aplurality of PtM paging occasions that are each associated with a numberof wireless transmit/receive units (WTRUs) that does not exceed athreshold selected such that the paging occasions are not saturated;activating a point-to-multipoint (PtM) service for a PtM service usergroup of WTRUs that includes a number of WTRUs that exceeds thethreshold; and defining paging subgroups of the WTRUs within the PtMservice user group based on the established PtM paging occasions bygenerating a plurality of subgroup paging identities such that eachsubgroup paging identity is associated with a particular pagingsubgroup, a particular paging channel and one of the established PtMpaging occasions.
 2. The method of claim 1, wherein a physical pagingchannel is selected from a list of paging channels by determining aselected paging channel number based on a temporary identity mod K,where K is the number of physical paging channels that exist within acell.
 3. The method of claim 2, wherein a unique radio frame numberidentifies a particular paging occasion on the selected physical pagingchannel, the unique radio frame number being determined as a function ofa temporary identity div K and a discontinuous reception (DRX) cyclelength.
 4. A radio network controller (RNC) for paging a plurality ofwireless transmit/receive units (WTRUs) belonging to a paging group, theRNC being configured to: establish a plurality of PtM paging occasionsthat are each associated with a number of wireless transmit/receiveunits (WTRUs) that does not exceed a threshold selected such that thepaging occasions are not saturated; activate a point-to-multipoint (PtM)service for a PtM service user group of WTRUs that includes a number ofWTRUs that exceeds the threshold; and define paging subgroups of theWTRUs within the PtM service user group based on the established PtMpaging occasions to generate a plurality of subgroup paging identitiessuch that each subgroup paging identity is associated with a particularpaging subgroup, a particular paging channel and one of the establishedPtM paging occasions.
 5. The RNC of claim 4, wherein a physical pagingchannel is selected from a list of paging channels by determining aselected paging channel number based on a temporary identity mod K,where K is the number of physical paging channels that exist within acell.
 6. The RNC of claim 5, wherein a unique radio frame numberidentifies a particular paging occasion on the selected physical pagingchannel, the unique radio frame number being determined as a function ofa temporary identity div K and a discontinuous reception (DRX) cyclelength.
 7. An apparatus for facilitating paging wirelesstransmit/receive units (WTRUs) comprising: a paging control componentconfigured to establish a plurality of PtM paging occasions that areeach associated with a number of wireless transmit/receive units (WTRUs)that does not exceed a threshold selected such that the paging occasionsare not saturated; the paging control component configured to activate apoint-to-multipoint (PtM) service for a PtM service user group of WTRUsthat includes a number of WTRUs that exceeds the threshold; and thepaging control component configured to define paging subgroups of theWTRUs within the PtM service user group based on the established PtMpaging occasions to generate a plurality of subgroup paging identitiessuch that each subgroup paging identity is associated with a particularpaging subgroup, a particular paging channel and one of the establishedPtM paging occasions.
 8. The apparatus of claim 7 wherein the pagingcontrol component is a radio network controller (RNC).
 9. The apparatusof claim 7 wherein the paging control component is configured to selecta physical paging channel selected from a list of paging channels bydetermining a selected paging channel number based on a temporaryidentity mod K, where K is the number of physical paging channels thatexist within a cell.
 10. The apparatus of claim 9 wherein the pagingcontrol component is configured to use a unique radio frame number toidentify a particular paging occasion on the selected physical pagingchannel, the unique radio frame number being determined as a function ofa temporary identity div K and a discontinuous reception (DRX) cyclelength.